| 摘要 |
A phase-shifting alignment system for aligning a wafer in a stepper comprises a light source emitting a beam with a wavelength; a plurality of grating stripes formed on the wafer, wherein when the beam from the light source is incident upon the grating stripes, the wafer reflects a diffraction beam; a filter unit positioned on the optical path of the diffraction beam, such that the diffraction beam travels through the filter unit so as to generate a convolution beam; a positive lens having a front focal length, a back focal length and an optical axis and positioned on the optical path of the convolution beam so as to generate Fourier transform of the convolution beam at the back focal length, wherein the distance between the positive lens and the filter unit is the front focal length; and an image-receiving means positioned at the back focal length of the lens so as to receive the Fourier transform of the convolution beam on the optical axis of the lens.
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